(1) Field of the Invention
The invention relates to grid-like element and a screen device therefor for insertion into a vibrating shaker for filtering solids out of a moving fluid stream passing thereacross.
(2) Brief Description of the Prior Art
In the drilling, completion, workover, or the like of a subterranean oil and/or gas well, or water well, or in conjunction with a mining operation for the recovery of one or more minerals or other solids, a fluid, such as an aqueous or oil based carrier fluid is used in the operation. For example, during the drilling of a subterranean well, a drilling fluid, which may be aqueous-based, is introduced into the well during the drilling operation, usually through a drill string extending therethrough having at its lower-most end a drill or other cutting devise through which there are passageways defined extending to the hollow interior of a substantially cylindrical string of tubing. This "drilling fluid" does include, of course, numerous chemicals, such as flocculants, coagulants, and/or thixotropic materials for purposes of providing numerous chemical and physical characteristics to the fluid. As the fluid is discharged through the openings through the drill bit secured to the lower-most section of tubing, it circulates upwardly around the exterior of the tubing and carries with it cuttings and other particulate material resulting from the penetration of the bit and drill string through the earth. It is preferable to re-cycle this fluid to separate the solid particulate matter therein from the base fluid stream. This is effected at the top surface of the well by using one or more of a number of well known solids-separating pieces of equipment, such as centrifuges, shaking devices, and the like. Most typically, the top surface separating system will include the vibratory or other shaker means having affixed thereto in a number of well known prior art ways, one or more screen devices. The shaker device is vibrated in continuous or varying patterns such that the solids which are larger than the screen mesh move across the shaker which has below the screening surface a trough for collecting the cleaned fluid stream and reciprocation of such stream through the well. The shaker agitates the screen such that the fluid stream is permitted to pass through the screen device, but particulate matter at the "cut" point, i.e., over a given size, is effectively separated therefrom and removed from the top surface of the screen in one of a number of conventional ways.
Additionally, many prior art screen devices have been provided which have a series of small mesh openings through wire or other elements extending thereacross to define the openings in the screen. This screen is typically secured to a grid-like structure for support thereof, with the grid-like structure having openings therethrough comparatively larger than the openings through the screen elements.
As contemplated herein, such screens may be of the repairable type in which a patch or other element is provided to replace a portion of the screen by cutting out the screen portion through the openings of the grid-like structure, or otherwise repairing same. Likewise, the present invention contemplates use of a permanent, or non-repairable screen. The present invention is equally compatible with each such type.
Some prior art grid-like structures may be those as shown in FIGS. 1 and 1a of U.S. Patent Application entitled "Repairable High-Conductance Subterranean Well or Mining Screen Device for Vibrating Shakers" filed on Apr. 8, 1993 with the United States Patent and Trademark Office, Jeffrey E. Walker and Robert L. Dugal being the inventors thereof, and assigned to Advanced Wirecloth, Inc., Ser. No. 08/045,489, and as shown in FIGS. 1 and 1a of the present application.
In such prior art structures, there is a lack of strength and continuity across the face of the grid such that the small cross-members, P-1 and P-2 as shown in FIGS. 1 and 1a herein break or rupture. Additionally, such small members render the entire device subject to fatigue failure, and the like.
By application of the present invention, the unique geometrical design of the openings eliminates the need for excess tension placed on the wirecloth prior to bonding to a solid frame. The naturally occurring expansion and contraction of the grid-like structure may automatically tension the mesh filtering screens thereacross. This factor substantially reduces the cost of manufacturing, when the manufacturing procedure is stamping, by reducing the time required per grid-like structure. Also, the present invention eliminates the need to cut wire-mesh oversized to facilitate being filtered into a stretching device which, in time, reduces the overall amount of wirecloth consumed.
For a typical 1".times.1" inch pattern prior art screen, the total effective opening through the grid is 6.60 S.F. A typical prior art screen and grid of 2".times.2" will yield a total effective opening through the grid of 8.012 S.F. Likewise, a 3".times.3" screen with prior art grid will yield a total opening through the grid of 8.80 S.F.
A 1".times.1" alternate prior art grid and screen cloth will have total opening through the grid of 7.91 S.F. A second alternate prior art screen of the same pattern as that above will contain 2".times.2" of screen with grid total opening therethrough of 8.76 S.F. In comparison, the preferred embodiment of the present invention, in triangular form, has a total square opening through the grid of 1.292" and a total effective opening area through the grid of 8.52 S.F. Therefor, it can be seen that the preferred triangular embodiment of the present invention has a total effective opening of 8.52 S.F. which exceeds the 1 sq. inch and 4 sq. inch. openings of the first prior art devices and is just slightly less than the 3".times.3" "first prior art device total opening" of 8.80 S.F. Likewise, in comparison with the alternate first screen having a 1 sq. inch effective opening through the grid, the preferred embodiment of the present invention in triangular format has a total opening area of 8.52 S.F., considerably more than the 1 sq. inch alternate second prior art version and almost approaching the total opening area of 8.76 S.F. defined in the 4 sq. inch second alternate prior art device.
It should be appreciated that the grid-like structure of the present invention has enhanced strength and more effective opening area therethrough. However, the grid-like structure is not provided as a tensioning means for the screen mesh secured thereacross to the upper face thereof.